This disclosure is related to the field of bladed rotors generally, and more specifically to integrally bladed rotors.
Bladed rotors such as impellers, blisks, etc. are employed in gas turbines and other machines. The design, construction and materials of bladed rotors often dictate operating limits for the turbines in which they are employed. Extensive efforts have been made over the years to develop new alloys, new fabrication techniques, and new component designs which permit operation of these rotors at higher operating temperatures and/or lead to lighter weight, longer lived components, with all their attendant advantages.
The fan, turbine, and compressor sections of gas turbine engines include one or more circumferentially extending rows or stages of airfoils, commonly called rotor blades, which are axially spaced between rows or stages of fixed airfoils (stator vanes). The rotor blades are connected to and extend radially outwardly from a rotor disk. During operation the centrifugal loads generated by the rotational action of the rotor blades must be carried by the rotor disk within acceptable stress limits.
In one type of a conventional bladed rotor assembly, the rotor disk has a plurality of slots around its radially outer periphery. The blades may comprise a root, a platform, and an airfoil. The platform has opposite facing surfaces. The root attaches to the slot in the disk and the airfoil extends radially out from the disk. The slots and the roots have complementary shapes, typically either a dove tail or a fir tree. The root mates with the slot and the blade extends radially outward therefrom. This type of rotor assembly is relatively heavy because the slots are cut through the rim of the disk creating what is called a “dead rim” where the metal between the slot can pull on the disk with well over 10,000 g's and fir tree or dovetail mating structures likewise do not contribute to sustaining the disk's centrifugal load and also pulls with the same 10,000 g load, thereby necessitating that the rotor disk be sufficiently sturdy, and thus heavy, in order to accommodate the stresses resulting from the heavy blade attachment area.
Alternatively, the blades may be secured by bonding or welding, to the rotor disc to thereby form an integrally bladed rotor assembly (IBR). A major advantage of an integrally bladed rotor assembly is that there is often no need for an extended blade root or a blade platform. The airfoil may be secured directly to the radially outer periphery of the rotor disk. The absence of an extended root and a blade platform results in a blade that is lighter than a conventional blade. A lighter blade enables the use of a less rigid and lighter rotor disk, in which case the integrally bladed rotor assembly is overall much lighter than a conventional bladed rotor assembly.